Anode structure for double filament x-ray tube



Oct. 16, 1956 2. J. ATLEE 2,767,341

ANODE STRUCTURE FOR DOUBLE FILAMEINT X-RAY TUBE 2 Shets-Sheet 1 Filed Aug. 12, 1952 INVENTOR.

ZED J; ATLEE AT TORNEYS AMENT- X-RAY TUBE,

2 eets-Shee't 2 Z. .J. ATLEE FOR DOUBLE FIL United States Patent 9 AN ODE STRUUI'URE FOR DOUBLE FILAMENT X-RAY TUBE Zed J. Atlee, Chicago, 111., assignor to Dnnlee orp., Chicago, 111., a corporation of Illinois Application August 12, 1952, Serial No. 393,945

7 Claims. (Cl. 313-56) The present invention relates to X-ray generators and more particularly to an anode structure for an X-ray tube of the double filament type.

In my copending patent application, Serial No. 197,441, filed November 24, 1950, now United States Patent No. 2,671,867, issued March 9, 1954, entitled Electrode Structure for X-Ray Tubes, I have described an electrode arrangement whereby the ratings of an X-ray tube may be greatly increased. For example, the ratings of a tube made in accordance with that patent, when oper ated self-rectified, are increased substantially to the fullwave rectified rating of the tube with a heretofore conventional electrode arrangement. This is accomplished, according to one modification, by the relatively simple expedient of tilting the anode face in the direction laterally of the longitudinal direction of the filament whereby the inverse electrons emitted from the anode face impinge harmlessly against the cathode head to one side of the filament and which is thereby safeguarded against destruction. Accordingly, the tube ratings may therefore be considerably increased as compared with those of conventional tubes.

The above mentioned prior application is concerned primarily with single filament X-ray tubes and it is a general object of the present invention to provide similar advantages in an X-ray tube of the double filament, or double focus type with an electrode arrangement whereby both of the filaments will be protected against the inverse electron flow.

As described in the above mentioned copending application, it has been my observation that the electrons emitted from the heated target of an X-ray generator, which electrons may for convenience be termed inverse electrons, fiow in a path perpendicular to the face of the target. In conventional tubes, in which the filaments are in line with the perpendicular of the corresponding anode spots, the inverse electrons will impinge upon the heated filament. Accordingly, when the tube is operated in a self-rectified manner, the electrons generated at the target impinge upon the filament during the inverse half cycle of the applied potential. These inverse electrons cause increased heating of the filament which in turn results in increased emission of electrons from the filament to result in still greater heating of the target. This, of course, further increases the inverse electron emission from the target creating a runaway condition of the tube that may result in destruction of the cathode filament.

It is an object of the present invention to provide a double filament type of X-ray generator in which the cathode and anode are so arranged that the cathode filaments are protected against destructive inverse electron emission from the anode.

A more specific object of the invention is to provide an X-ray generator of the double filament type in which the relative angular relation between the facing ends of'the cathode and anode is such that the inverse electron emission from the anode focal spot of an energized "ice filament is directed in a laterally displaced relation with respect to the energized filament.

Other objects and advantages of the invention will become more apparent hereinafter.

The X-ray generator of the present invention includes a cathode unit having a pair of spaced-apart, longitudinally parallel cathode filaments focused to have their focal spots longitudinally parallel and relatively closely adjacent one another upon the anode target. A V-shaped target element mounted on the anode includes portions defining a separate planar target area for each of the electron beams generated by the cathode filaments, theface of each of the portions defining a plane inclined in a direction longitudinally of the corresponding cathode filament and, in addition, inclined at a second angle of inclination in a direction at right angles with respect to the first angle, the second angle of inclination being such that inverse electrons from the focal spot on the particular portion impinge harmlessly against the cathode structure in a laterally displaced relation with respect to the energized filament.

For a consideration of What is believed novel and inventive, attention is directed to the following description taken in connection with the accompanying drawings, while the features of novelty will be pointed out with greater particularity in the appended claims.

In the drawings,

Fig. 1 is a longitudinal elevation, partly in section, of a double filament X-ray generator embodying the present invention;

Fig. 2 is a fragmentary view of the anode and cathode parts taken along line 22 of Fig. 1;

Fig. 3 is a partial sectional view of the cathode and anode units taken along line 33 of Fig. 1;

Fig. 4 is a sectional view taken along the line 4-4 of Fig. 3;

Fig. 5 is a partial sectional view of the anode head taken along line 55 of Fig. 4;

Fig. 6 is an end view of the anode head taken along line 66 of Fig. 4; and

Fig. 7 is an end view of the cathode head taken along line 77 of Fig. 3.

The present invention is illustrated in connection with an X-ray generator or tube comprising coaxially mounted anode and cathode units 13 and 14 sealed within an envelope 17 preferably formed of glass.

The anode 13 is suitably mounted in the envelope 17 and sealed therein at one end of the envelope by a glassto-metal seal 19 through which a portion 20 of the anode extends outwardly of the envelope to provide for cooling the anode.

The cathode unit 14 is likewise sealed in the envelope, preferably by a glass-to-metal seal 21 at the end of the envelope remote from the seal 19, the cathode being connected Within the envelope to conductors 23 extending outwardly of the envelope through the seal 21 for the purpose or" energizing the cathode from a suitable source of energizing current.

Referring particularly to Figs. 3 and 7, the cathode head facing the anode is provided with a pair of cathode means comprising a pair of elongated, longitudinally parallel electron focusing cup recesses 24 and 25 formed in the surface thereof facing the anode unit and in which are disposed the electron emitting filaments 26, 2? respectively which extend longitudinally of the cups. The filaments 26, 27 are suitably connected with the conductors planar portions being angularly inclined with respect to the direction of said filaments.

6. In a double filament X-ray tube of the class described, an anode unit having a pair of reentering planar X-ray emitting surface defining portiens, said planar portions being disposed at an angle of less than 180 with respect to each other.

7. A dcuble focus X-ray generate-r comprising a cathode unit having a pair of substantially parallel, laterally spaced apart, elongate filaments, and ode unit hav ing an indented, unitary target elem M a pair of target areas angularly inclined tcward each other.

References Cited in the file of this patent UNITED STATES PATENTS Thomas Ian. 26, Bouwers June 11, Mutschellcr Dec. 10, Slack Aug. 1, Langhans Mar. 8, Atlee Sept. 14, Hultquist Feb. 12,

FOREIGN PATENTS Netherlands Nov. 15, 

